I’ve been asked to comment on many views for planning and
it’s surprising how often I’m called in because someone in the team says,
“The AVRs just don’t look right.”

I used to get pretty defensive about this remark on behalf
of the architectural visualisation (or archviz) community. The renders often
looked great, so the arrogant nerd in me would always want to fold his arms,
pull a wry smile and tell the doubters that the work was good, and if they
couldn’t see it, then maybe that said something about them. And worse, if a non-archviz
(ie normal) person complained that the “perspective looks distorted”, honestly,
I would suppress a scream.

But, after a long conversation with a particularly nice (read:
patient) client who’d studied photography, so she knew what she was talking
about, I looked again. Whether we, the ‘makers’ of these images are right or
not, if the ‘users’ – the teams that rely on verified views during planning
applications – think they look off, then it’s our duty to address the issue.
Whether we agree or not.

As I see it, this perceived “wrongness” comes down to two
issues.

1.
The use, or not, of tilt-shift lenses

2.
Fields of view, or more accurately angles of
view.

Now, even from all the way over here where I sit at my
keyboard, at least two screens and the internet away from you, I can see your
eyes glazing over; the curled lip of a stifled yawn. But there’s an important
reason why you might want to stay with me on this. Promise.

1. Tilt-shift lenses

A tilt-shift lens lets us get the top of a building into the
frame without tilting the camera. When a camera is tilted, a simple perspective
of two vanishing points becomes three vanishing points and all the verticals
converge to that third point. Everything goes wedge-shaped.

It’s not just that we’re used to two-point perspective
from every oil painting ever, but our brains – which receive images from the
eye in three-point perspective on a curved surface – correct it for us too in
the process of making the world less nauseating to navigate. As a result an
uncorrected three-point perspective image can look distorted on the page or screen.
It doesn’t match our perception of the real world. In reinstating the order of
two-point perspective, a tilt-shift lens goes some way to matching the remapping
our brain undertakes.

But even a corrected perspective can look distorted. As the
tilt-shift lens moves the horizon down the page, the tops of
objects get increasingly wide-angle and pointy. The square corner of a
skyscraper for example, can turn into a knife edge.

The reason for this is angle of view.

2. Angles of View

A while back (1995 or so) we were asked to build a ‘mini-Imax’
theatre for a property client, and render an immersive walkthrough of their proposal
to run on it. I knew we’d have to render multiple panels for each frame of
animation (this was before HD) and join them together to fill a screen that
size, but how many panels, and more importantly what view angle did we render to
fill the audience’s vision?

The total angle we can see is about 120-degrees, so if projected images span 150-degrees then our peripheral vision is filled. Once
this happens, we are tricked into feeling as if we are within the frame.

We managed this with three stitched together panels for each
frame, and the effect of our first experiments were so powerful our clients had
to hold onto their chairs to stop themselves falling over when the animation moved. The
(calmed down!) version was compelling enough that the building was let before
it was built, and off the back of it Foster and Partners asked us to create an
immersive experience, this time filmed, of Chek Lap Kok airport.

So you would think that an image of 120-degrees would be
optimal, and it would if we were to print it out and stand in just the right
place to have it fill our vision. But this is rarely practical. We have to
accept that anything less than filling our vision is a compromise of some kind,
and the difference in perception is huge.

Photographers have determined that for most purposes the
normal or standard lens, with a view angle of around 40-degrees to 60-degrees, represents
the most natural perspective in terms of the least distortion and best separation
between foreground and background.

Why this might be is up for debate. Some say it’s when the
distance between observer and object equals the diagonal field of view at the
object's plane. Others say it’s because a photographic print of something in
this range can be held up, at arm’s length, to overlay the real scene. Some say
it’s just an accepted standard based on lenses originally shipped with the most
common cameras, and we’ve just become used to it.

(Interesting side note: The latter is backed up when perspectives
are shown to people who’ve never seen a perspective representation of the real
world; they have difficulty understanding it at all. Also, in the early days of
cinema, any change of lens angle was considered confusing, so most movies where
produced with one or two lenses. The range of representation, or distortion,
that we can understand is definitely increasing. This might explain why people
who work with perspective get frustrated with those that don’t. Though why those
that don’t understand perspective seem to be in charge of all the money is
still a mystery.)

Whatever the reason, 40-degrees to 60-degrees is an accepted
standard to the extent that anything outside this range can be legally challenged
as distorting the scene.

Here, you can see the effect of crossing a road and using a wider angle. The furthest camera position in this video uses a 45-degree lens. By standing closer to the foreground building, and using a wider lens so the smaller building stays the same height in the frame, the tower appears to shrink to insignificance.

For urban settings, the standard lens is quite a restricted frame and it's not always practical to move the camera back to get more into the frame. In this case, photographs are taken with a wider lens to capture more context and markers on the border describe where the 40-degree limit lies. If the
images don’t have these markers, (or graticules if you want to sound like an
expert) then they are not professional planning views and should be questioned. If that
step’s been missed out, then what other shortcuts have been taken?

Likewise if you ask what the view angle is, and you get a
shrug and/or “It’s a 24mm lens on a Canon DSLR with a whatever up its whatever”
and they don’t know what that means in terms of the view angles of human eyesight, then they haven't considered the issue. I would find that worrying.

Either way, if a view looks off, the first thing to do is always to crop
it to the 40-degree mark, print it at A3 and hold it at arm’s length. Geometrically,
at least, this is as close as you will get to looking (out of a little window)
at the proposal.

Also our angle of vision might be 120-degrees horizontally but
it’s only 80-degrees vertically. What we can take in peripherally side to side,
we have to look up to take in vertically. So not only will the perspective of a
tower be increasingly distorted, the further from the 40-degree marker it lies,
the more looming it will appear in real life. Above 80-degrees and we’re
craning our neck.

So beyond some people feeling that CGIs for planning look a little
“off” why should we care? Everyone knows that estate agents have used wide-angle
photography for years, to make a kitchen with a sofa in it look like a spacious
studio apartment. We expect this visual white lie, and make allowances for that
fact we’ll be disappointed when we come to viewing the property in real life. No
biggie.

But when buildings are built, and they make a much more
imposing impact than we imagined. When they loom over us, where all the
verified views showed them as something over there, not right in our face, then
perhaps we should care.

And if no-one cares enough to double check this, if we glaze
over and dismiss it, then perhaps that suits those who might wilfully use view
angles to mislead. Ask yourself how many times you’ve been surprised by how big
a development seems, next to the visuals. And are you OK with this?

Perhaps, and call me paranoid if you want, whenever we
ignore something because it sounds complicated and arcane, there is someone,
somewhere, glad we’re not paying attention.

This blog is dedicated to my kids who often complain they
will never use their GCSE maths in ‘the real world’. It’s also to remind me to
keep on squirrelling away that apparently useless information...

A family friend studies drawing and painting at the
Barcelona Academy of Art. She’s being taught – or re-taught as she was already
an artist – to paint in the way of the grand masters; a tradition of realism that
goes back to the renaissance. Being from the polar opposite world of computer
rendering I’m continually blown away by her work and whenever she describes her
techniques I’m like the HMV dog. I always hope that some of her analogue wisdom
might add some different dimension to my own, digital, work.

Now call me stupid, but there was one thing she told me that
seems so obvious I don’t know why I never worked it out. She paints from life,
from models or sculptures, and will always position her easel the exact distance
required to create a 1:1 relationship between her canvas and the subject. To
fit the subject onto, say, an A3 canvas she’ll stand right next to a marble
bust but might be several feet away from a human figure. Then all she has to do
is transcribe everything like-for-like, without having to scale anything up or down.

This stuck in my head even though I had no actual use for
the information at the time.

Then, working on the planning application for Herzog de
Meuron’s Blavatnik School of Government in Oxford, I was asked to produce some
verified views: accurate photomontages that showed the new design in relation
to landmarks when viewed from a distant vantage point. Some residents were
worried that the proposals unusual form would distract from the historic skyline. The
scheme looked very small on the photomontages, even accounting for the
‘standard’ lens we used to closely approximate the human eye’s angle of view.
Even when we produced a set with a zoom lens to mimic the eye’s ability to
focus in on details.

Both these approaches were in keeping with the industry
standard method for creating accurate visual representations (or AVRs... It’s
not clever unless it has an acronym). Still, the residents naturally wanted us
to produce a set of large blow-ups, complaining the scheme wasn’t clear enough on
the photomontages for them to judge its impact on the vista. Was it the case
that, if they couldn’t make out the scheme in the images, then perhaps the design
wasn’t a problem in real life? It fell on us to come up with a credible way to
put their minds at rest.

I remembered my artist friend and her easel, and wondered
what size you would need to print a standard lens photograph, and how far you’d
have to stand from it, so that the scale of it matched its real-world scale.
The answer lay in some surprisingly simple trigonometry. See Figure 1.

So if our photograph was taken on a medium format camera with
a 47mm lens, that gave us a horizontal view angle of around 54-degrees which we
usually cropped to 40-degrees. Printed at A1 – 831mm wide – if you stood 1140mm
from the print it would cover a 40-degree portion of your vision and everything
in the image should be the same “size” (subtend the same angle) as the real
world as seen from the camera’s position.

We printed the verified views to size and our client hung
them for the residents with instructions to debate from the prescribed distance,
and... the Blavatnik School of Government is a fantastic building which you can
still see to this day. In actual fact, there is a statue of me outside it in
commemoration of my genius and my project-critical input.

Only one of those assertions is true.

Still, here’s the generalised equation if you’re interested:

Viewing distance from image=Half image width/TAN(half
view angle)

It’s thrown up some surprising (to me) ‘did you knows’. Did
you know that a 40-degree photo printed at A3 and held at arm’s length (approx.
57cm) will match the perspective of the real world? As will an A4 print of an
iPhone photo held at just under an A4’s length from your face?

These days, I print renders at A4 (with a 30-degree view)
and use them on site walk-arounds to help determine where a proposal will
appear when it’s built. Everybody is delighted and impressed when I repeatedly
shove images in their faces at exactly the right distance for the perspective
illusion to spring into life.

I don’t know why this technique of printing to scale isn’t
used by more people more often; in site visits or brochures or on hoardings. I like to think of it as a kind of digital
trompe l’oeil or a printed projection map. Or an Augmented Reality head-up
display. Old school.